The invention relates to a trench transistor having an active zone enclosed by an edge trench, wherein an edge electrode at gate potential is embedded into the edge trench, and the active zone has a mesa structure at least partly adjoining the edge trench. The invention furthermore relates to a method for producing a trench transistor of this type.
Trench transistors of the type referred to above are also referred to as trench transistors having a “closed design”. FIG. 1 illustrates a basic schematic diagram of a possible embodiment of a trench transistor having a closed design (plan view). The illustration illustrates an active zone 1 of a trench transistor, enclosed by an edge trench 2. The active zone 1 has a mesa structure, which in this case includes a plurality of mesa strips 3 arranged parallel to one another. The mesa strips 3 are separated from one another by gate trenches 4.
FIG. 2a illustrates a perspective illustration of the region identified by “D” in FIG. 1. The illustration additionally illustrates a part of an edge termination 5 which at least partly surrounds the active zone (to put it more precisely the edge trench 2). The edge termination 5 includes a plurality of mesa strips (oxide edge) 3′ which are coated with an insulation layer (field oxide layer) and are separated from one another by edge termination trenches 6.
FIG. 2a illustrates a process stage of the trench transistor before a field electrode structure composed of a plurality of field electrodes 7 insulated from the semiconductor body 9 by using a field oxide layer 8 (see FIG. 2b) is embedded within the trench structure (including edge trench 2 and gate trenches 4). The field oxide layer 8 is produced by oxidation of the entire semiconductor body 9 and subsequent etching back of the oxide layer thus produced into the trench structure. The free spaces remaining between the field oxide layer regions are filled with electrically conductive material (e.g., polysilicon) in order to produce the field electrodes 7. The semiconductor body 9 (at least the mesa structure) is then oxidized anew in order to produce a gate oxide layer 10, free spaces that remain between the gate oxide layer regions being filled with electrically conductive material (e.g., polysilicon) in order to produce a gate electrode structure composed of a plurality of gate electrodes 11. Afterward or before the formation of the gate oxide layer 10, source zones S and body zones B are produced within the mesa strips 3, the zones reaching to the end sides 12 of the mesa strips 3. The trench transistor outlined schematically in FIG. 2B is thus produced (FIG. 2b illustrates a reduced cross-sectional illustration of the trench transistor illustrated in FIG. 2a along the sectional line A, but in FIG. 2a the trench fillings have been omitted in order to better illustrate the individual trenches).
With the trench transistor illustrated in FIG. 2b, at the end sides 12 on account of the gate electrode 11 provided within the edge trench 2 and on account of the source and body zones S, B reaching to the end sides 12 of the mesa strips 3, channels can be produced within the body zone B, that is to say that at the end sides electric currents are induced between the source zone S and the semiconductor body 9 if the gate electrode 11 is at gate potential together with the gate electrodes 11 provided within the gate trenches 4. The electric currents at the end sides 12 are undesirable, however.
In order to avoid the electric currents at the end sides 12 it is known, for example, for the source zones S not to be permitted to reach to the end sides 12, but rather for only body zones B to be formed in those regions of the mesa strips 3 which adjoin the end sides 12. For this purpose, in the prior art, a dedicated source photomask is used for example during the production of the source zones.
In this case, however, the production of the source zones S thereby becomes unnecessarily complicated.